This invention relates to a corona generating device having an improved cleaning apparatus incorporated therein for cleaning the device.
In the practice of xerography as described in U.S. Pat. No. 2,297,691 to Chester F. Carlson, a xerographic surface comprising a layer of photoconductive insulating material affixed to a conductive backing is used to support electrostatic images. In the usual method of carrying out the process, the xerographic surface is electrostatically charged uniformly over its surface, and then exposed to a light pattern of the image being reproduced to thereby discharge the charge in the areas where light strikes the layer. The undischarged areas of the layer thus form an electrostatic charge pattern or electrostatic latent image in conformity with the configuration of the original pattern.
The latent electrostatic image is developed by contacting it with a finely divided electrostatically attractable material, such as a resinous powder. The powder is held in the image areas by the electrostatic field on the layer. Where the field is greatest, the greatest amount of material is deposited, and where the field is least, little or no material is deposited. Thus, a powder image is produced in conformity with the image of the original being produced. The powder image is subsequently transferred to a sheet of paper or other transfer member, and suitably affixed thereto to form a permanent copy.
The latest concept for electrostatic reproduction machines utilizes high speed flash exposure of the document, and a moving photoconductive material in the form of an endless belt which is continuously charged. Additionally, such reproduction machines are provided with a developing system which supplies toner particles in relatively large quantities for solid area coverage, such as a magnetic brush developing apparatus. Thus, after the belt passes the magnetic brush assembly, for example, a xerographic powder image is formed on the belt which corresponds to the electrostatic latent image. This powder image is then transferred to a support surface (e.g., a sheet of paper) to which it is fused by a fusing assembly whereby the powder image is caused to adhere to the support surface permanently.
These electrostatic reproduction machines include corona generating devices to effect certain functions, including for example, charging the xerographic surface prior to exposure, treating the electrostatic latent image prior to development, treating the developed electrostatic image prior to transfer thereof, and charging the xerographic surface to neutralize the charge on the residual toner particles prior to contacting the surface with a cleaning brush.
One particularly useful type of corona generating device is described in detail in U.S. Pat. No. 2,836,725 issued to Vyverberg. This device is usually comprised of at least one corona wire which is partially surrounded by a conductive shield. Although this corona generating device is adapted to provide a uniform electrostatic charge on the desired surface, dust or toner particles accumulating on the corona wire and shield can cause non-uniform generation of corona current along the length of the corona wire.
A variety of techniques have been devised to reduce or remove such contamination. These techniques are disclosed in U.S. Pat. Nos. 3,324,291, 3,339,069, 3,382,360, 2,471,965, 3,483,372, 3,496,352, and 3,499,143. To clean the corona wire and/or the shield of a corona generating device, numerous arrangements are available. IBM Technical Disclosure Bulletin, Vol. 8, No. 8, January 1969, discloses a cleaning apparatus for cleaning the corona wire only. U.S. Pat. Nos. 3,842,273, 3,870,833, and 3,891,846 disclose apparatuses for simultaneously cleaning both the corona wire and the shield of a corona generating device.
The creation of corona current is predominantly determined by the potential difference between the corona wire and the shield. Dust particles and toner particles which accumulate on the inner walls of the shield produce deleterious effects, particularly for a grounded metal shield. These particles are comprised of dielectric material which can store charged ions generated by current through the corona wire. As the charge builds up on these particles, a non-uniform potential difference between the corona wire and the shield is produced with consequent variations in corona discharge along the length of the corona wire. This latter problem is particularly associated with corona generating devices employing a metallic shield. For corona generating devices employing a dielectric shield, e.g., a plastic material such as Teflon or Mylar, the accumulation of such particles on the shield has no appreciable effect on the current uniformity.
Although the cleaning apparatuses disclosed in the last three patents discussed above may be quite satisfactory for removing the contamination from both the interior of the shield and the corona wire, it is difficult for the technical representative to replace these cleaning apparatuses since this requires removal and/or partial disassembly of the corona generating device. Cleaning apparatuses for corona generating devices ultimately become dirty and have be be replaced. Thus, what is needed, is a cleaning apparatus for a corona generating device which is capable of cleaning all of the interior surfaces of the shield and the corona wire, a cleaning apparatus which includes disposable portions which can be quickly and easily replaced without having a disassemble the device itself.